380 Head Gasket Issue

[al perna]

I have been reading over on wog about the issues the 380 owners seem to be having with blowing head gaskets . It would seem to me they should have some recourse with Comings or Blue Bird .
I know some of these guys and they take care of there coaches , so I do not see this as a user error issue .

[ernie ekberg]

I believe other coaches with that Cummins engine have had issues, also.

[davidbrady]

Thanks Al,

I don't know if you recall, but in 2012 when Chuck Millsap owned an M380 he started a database to track info on other owners in an attempt to quantify M380 Cummins ISL head gasket failures. I attached a copy of the excel spreadsheet. There were 74 M380's built and there are 52 buses represented on the spreadsheet with 5 of them experiencing head gasket failure. The new failure which Al speaks of brings the total to 6 known failures, so roughly 8%. There are likely additional failures that haven't been recorded to the list. I think there was one bus that had two head gasket failures. A failure rate this high implies a manufacturing or engineering defect. Whether it's a Cummins or a Blue Bird issue is still unknown. What's known in the latest case is that the engine experienced prolonged overheating as reported by the engine computer readout and that's being reported by Cummins as the likely cause of the failure. Turns out the M380 dash coolant temperature gauge isn't reliably showing over-temp conditions.

[davidbrady]

After letting this gasket issue sink into the old noggin for a bit, let me throw out something else M380 owners might investigate. I don't know the cooling setup on the M380's ISL so if owners wish to educate me I'd appreciate it. I'd focus on what's causing the overheating. I'd look at the supply line from the radiator to the water pump inlet. My LXi had a short section of hose that joined the coolant radiator return pipe to the water pump inlet. Guess what was inside that silicon elbow? A steel spring. Turns out BB was concerned about water pump suction collapsing that section of hose, and if that were to occur it'd be a very bad thing, effectively halting the flow of coolant thru the engine. The suction increases with coolant flow rate, so you can imagine an engine revving to 2500+ rpm and the increase in coolant flow rate and the consequent pressure drop at the pump inlet. Food for thought.

[JD33]

David, while I do not know about older M380's, my 07 does have the spring inside the elbow.
I recently changed the downshift/engine brake parameters on my coach and downloaded all codes and events at that time. There were no overheating events recorded in the ECM.
I do agree that this is perplexing.

[davidbrady]

Thanks Jim,

From a purely statistical point of view to me this looks more like a Blue Bird issue than a Cummins issue. The percentage of failures given the huge number of ISL's out there is miniscule while the percentage of failures within the M380 family is significant. Also, while the jake brake shift programming pre-select may be a contributing factor, it's most likely not the cause. If it were the cause we'd see a much higher percentage in the M380 family. Based on this I'd focus on systems that were engineered, manufactured, and implemented by BB which is primarily the entire cooling system. So far it looks like folks have mostly been focusing on the engine and not the BB specific items. People have been analyzing the head gasket failure pattern, the water pump pressure at high rpm's, the preselect of the transmission during engine braking and skipping the elephant in the room which is the overheating conditions taking place which Cummins has determined to be the cause of the current failure.

A centrifugal water pump won't produce more than about 2 to 3 bar of head pressure before it stalls, that's around 30 to 45 psi. Compare this to the 2500 to 3000 psi peak pressures during power stroke combustion. Likewise, the cylinder pressures during jake braking are an order of magnitude less than combustion peak pressures. For example, the jake on the S60 will produce 15 psi of turbo boost. That's 15 psi from the atmosphere plus 15 from the turbo times a 16:1 compression ratio which equals about 500 psi of cylinder pressure, again far short of peak combustion pressures. While I wouldn't discount anything yet it's hard to imagine water pump pressures or jake brake pressures playing any significant role in gasket failure.

Which leaves the coolant circuit. It'd be very interesting to know if the latest failure has the spring in the water pump supply coolant hose. Here's what I'd do. I'd instrument the cooling system. How 'bout rigging it so the t-stats are always open (don't remove them just open them or find some other method to ensure they're open, removing them may take away a needed restriction in flow). We could pull the temperature sensor on the head and insert a pressure gauge or find a port on the back of the head to record pressure. Take off the fan belt and rig up an electric motor to spin the water pump. The water pump should only take a few horsepower to spin at max flow rate and head. Spin it up with the engine warmed up and at idle and note pressure at the head and note flow rates at the pump. Increase the speed of the pump until you hit the maximum 2900 engine rpm equivalent and see what the readings are and what the overall condition of the hoses and connections are. You could even read pressure before and after the pump to make sure you're not anywhere close to cavitation or stall. This to me would be a stress test of the cooling system's flow and pressure.

I don't think we're going to get anywhere on this problem without instrumenting and collecting measurements.